Long-Term Debt - Outstanding Long-Term Debt (Phantoms) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.54%
Proceeds from issuance of long-term debt	$ 99.5	$ 627.0	$ 49.9
5.93% note, due October 31, 2023
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Oct. 31, 2023
5.68% note, due June 30, 2026
Debt Instrument [Line Items]
Long-term debt, interest percentage	5.68%
Debt Instrument, Maturity Date	Jun. 30, 2026
6.43% note, due May 2, 2028
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.43%
Debt Instrument, Maturity Date	May 02, 2028
3.73% note, due December 16, 2028
Debt Instrument [Line Items]
Long-term debt, interest percentage	3.73%
Debt Instrument, Maturity Date	Dec. 16, 2028
3.88% note, due May 15, 2029
Debt Instrument [Line Items]
Long-term debt, interest percentage	3.88%
Debt Instrument, Maturity Date	May 15, 2029
Uncollateralized Senior Note Due on Two Thousand Thirty Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Apr. 30, 2032
Uncollateralized Senior Note Due May Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	3.48%
Debt Instrument, Maturity Date	May 31, 2038
Uncollateralized Senior Note Due November Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	3.58%
Debt Instrument, Maturity Date	Nov. 30, 2038
Uncollateralized Senior Note Due August Two Thousand Thirty Nine [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	3.98%
Debt Instrument, Maturity Date	Aug. 20, 2039
Uncollateralized Senior Note Due December Two Thousand Thirty Four [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	2.98%
Debt Instrument, Maturity Date	Dec. 20, 2034
Uncollateralized Senior Note Due July Two Thousand Thirty Five
Debt Instrument [Line Items]
Long-term debt, interest percentage	3.00%
Debt Instrument, Maturity Date	Jul. 15, 2035
Uncollateralized Senior Note Due August Two Thousand Thirty Five
Debt Instrument [Line Items]
Long-term debt, interest percentage	2.96%
Debt Instrument, Maturity Date	Aug. 15, 2035
Uncollateralized Senior Note Due April Two Thousand Thirty Two [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	3.25%
Equipment Security Note
Debt Instrument [Line Items]
Long-term debt, interest percentage	2.46%
Debt Instrument, Maturity Date	Sep. 24, 2031
Uncollateralized Senior Note Due January Two Thousand Thirty Seven
Debt Instrument [Line Items]
Long-term debt, interest percentage	2.49%
Debt Instrument, Maturity Date	Jan. 25, 2037
Uncollateralized Senior Note Due March 15, 2042
Debt Instrument [Line Items]
Long-term debt, interest percentage	2.95%
Debt Instrument, Maturity Date	Mar. 15, 2042
Uncollateralized Senior Note Due March 14, 2038 [Abstract]
Debt Instrument [Line Items]
Long-term debt, interest percentage	5.43%
Debt Instrument, Maturity Date	Mar. 14, 2038
Uncollateralized Senior Note Due December 2026
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.39%
Debt Instrument, Maturity Date	Dec. 31, 2026
Uncollateralized Senior Note Due December 2027
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.44%
Debt Instrument, Maturity Date	Dec. 31, 2027
Uncollateralized Senior Note Due December 2028
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.45%
Debt Instrument, Maturity Date	Dec. 31, 2028
Uncollateralized Senior Note Due December 2030
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.62%
Debt Instrument, Maturity Date	Dec. 31, 2030
Uncollateralized Senior Note Due December 2033
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.71%
Debt Instrument, Maturity Date	Dec. 31, 2033
Uncollateralized Senior Note Due December 2038
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.73%
Debt Instrument, Maturity Date	Dec. 31, 2038
Uncollateralized Senior Notes Due On October 2029
Debt Instrument [Line Items]
Long-term debt, interest percentage	5.20%
Debt Instrument, Maturity Date	Oct. 31, 2029